1. Field of the Invention
This invention relates to a photo-sensitive glass and to a process for its production. The glass of the invention is sensitized, that means it reacts more sensitive to irradiation with UV-light and can be crystallized easier and with higher aspect ratios than a non-sensitized glass with equal composition. Furthermore, the sensitized glasses of this invention have smaller crystal sizes after irradiation and tempering than a non-sensitized glass with equal composition.
2. Description of Related Art
Photo-sensitive glasses are usually used for producing micro-structured bodies. Thereby initially a glass is produced, which is photo-sensitive. This photo-sensitive glass is irradiated with UV-light on defined positions. Subsequently, the irradiated areas, in which nuclei have formed due to irradiation, are transformed by tempering into areas with a crystalline phase, which better dissolves in an etching medium than the non-crystallized glass. Consequently, the thus processed bodies can be selectively etched with an etching solution, which normally comprises hydrofluoric acid. The light exposed areas are etched by the etching solution in the range of 20 to 50 times faster than the intact glass. The result is a structured body.
Photo-sensitive glasses are known from the prior art for a long time.
The photo-structurable glass described in document US 2011/0195360 A1 comprises comparably much boron, aluminum and potassium as well as little silicon. The amount of alkali metal oxides is very high in the glasses described therein, apparently for reducing the melting point, which is increased due to the high aluminum content. In combination with the low content of silicon dioxide this results in a compromised chemical resistance. Accordingly, a high proportion of zinc oxide is used for improving the chemical resistance. The composition of the glass is not precisely described in this prior art document; the specified ranges are very wide and do not allow any conclusion with regard to the exact proportions. Also the process of production of the glass is not described. The glass is not sensitized, it thus has not the cooling state of the glasses of this invention.
Also U.S. Pat. No. 2,971,853 describes photo-structurable glasses that are supposed to be completely light exposed and ceramized. It is aimed at transforming the formed metasilicate crystals in the direction of the disilicate stoichiometry—thus towards lower alkali metal contents—by further temperature treatment. Accordingly, the contents of sodium and potassium are very low in the glass described therein. Furthermore, the importance of boron and zinc for the glass composition was not recognized in the document. The glasses were melted under different redox-conditions, however only in laboratory scale (1 pound). Furthermore, the glasses described in the document are not determined for structuring but they are supposed to be completely ceramized after irradiation. Thus, a ceramic body is produced and not a structured glass body.
DE 10 2005 003 595 A1 describes optical elements and systems, which comprise photo-sensitive glass or photo-sensitive glass ceramic. The glasses may be oxidic glasses or chalcogenide glasses. The compositional ranges do not allow any conclusion with regard to specific compositions. Differences in refractive index are supposed to be induced by irradiation. The glasses are not supposed to contain any antimony. Other crystal stoichiometries are aimed at as compared to the present invention. The glasses may be melted under oxidizing conditions. However, there is no processing in the sense of a sensitization after the melt so that a high cooling state of the glasses has to be assumed. Apart from that, the glasses described therein contain very much sodium and halides and little lithium. The production of glass bodies is done via cutting and polishing of a bulk glass.
DE 10 2008 002 104 A1 describes a glass that has a crystal phase of spodumene or lithium disilicate. The glass is supposed to have a coefficient of thermal expansion, which is as low as possible. The composition described therein has relatively much zinc and aluminum and only a little amount of sodium. DE 1 696 473 describes a process for producing crystalline mixed-bodies. The underlying glass contains very much aluminum and zinc. DE 103 04 382 A1 relates to a photo-structurable body. The glass underlying the body contains high amounts of aluminum. Furthermore, the glasses contain only little nuclei source in relation to cerium. US 2008/0248250 A1 relates to a process for production of structured glass structures with a high an anisotropic etching rate ratio. The glasses described therein contain relatively little silicon, in total a lot of sodium and potassium, a lot aluminum and a lot of boron.
All prior art documents have in common that the described glasses are in a high cooling state, thus have not been subjected to any sensitization. None of the documents suggests cooling the glasses slowly after the melt or subjecting the glasses to a controlled cooling step (sensitization) in a separate processing step after the melt. This would eventually also be against the experience of the skilled person that aims at a fast passage through the crystallization range (quenching) of such a crystallization-sensitive glass. As far as an increased crystallization tendency was aimed at in the prior art, this was tried to be achieved by adaptation of the compositional ranges, in particular of the nucleating agents. Improving the structurability by reducing the cooling state has not been suggested by the prior art.